Optical sensor with co-located pressure and temperature sensors

ABSTRACT

An optical sensor ( 10 ) that provides for concurrent pressure and temperature measurements at substantially the same location includes at least one launch fiber ( 22 ) and at least one temperature sensitive material ( 52 ) having a refractive index that changes with a change in temperature. The launch fiber and temperature sensitive material are spaced from each other across a gap ( 21 ) having length (L). A reflecting fiber ( 26 ) can be provided adjacent the temperature sensitive material. The optical sensor ( 10 ) also includes a sealed cavity ( 20 ). The launch fiber ( 22 ) and reflecting fiber ( 26 ) can be attached to the tube and at least partially disposed within the cavity. Changes in pressure change the length (L) of the gap ( 21 ).

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part application ofco-pending U.S. patent application Ser. No. 10/653,996, filed on Sep. 4,2003 and of co-pending U.S. provisional patent application No.60/499,725, filed on Sep. 4, 2003. The entire disclosures of theseapplications are incorporated herein by reference.

FIELD OF THE INVENTION

This present invention relates to optical sensors, and more particularlyto fiber optic systems having at least two sensors located proximate toeach other.

BACKGROUND OF THE INVENTION

Optical fibers have become a communication medium of choice for carryinginformation, in particular for long distance communication because ofthe excellent light transmission characteristics over long distances andthe ability to fabricate optical fibers in lengths of many kilometers.The information being communicated includes video, audio or data. Theability to transmit data signals is utilized in applications where theoptical fibers are used as sensors. These sensors can be used to detectphysical or environmental conditions including pressure, temperature,position, vibration, acoustic waves, chemicals, current, electric fieldand strain, among other properties. The information obtained can be usedin system control and calibration, and is conveyed by polarization,phase, frequency, wavelength and intensity modulation.

Optical sensors can replace conventional sensors, such as resistancegages, thermocouples and electric or electronic gauges, because opticalsensors provide immunity to electromagnetic interference andleakage-to-ground problems. Optical sensors also eliminate inaccuraciesassociated with long, multiple, signal lead requirements, and enjoycompact size, light weight, high sensitivity and large scalemultiplexing.

Known optical sensor geometries include Fabry-Perot, Bragg-grating,Mach-Zehnder, Michelson and Sagnac, among others. If all of the sensingoccurs within the optical fiber, the optical sensor is an intrinsicfiber; therefore, the fiber acts as both a transmission medium and asensing element. If the fiber does not act as a sensing element butmerely acts as a transmission medium, the optical sensor is classifiedas an extrinsic sensor. In an extrinsic optical sensor, the opticalfiber transmits the light source to an external medium, for example air,where the light is modulated to provide the desired sensing ordetection. Optical sensors are also classified by the optical principlewhich they operate. Interferometric optical sensors utilize interferencepatterns between source light beams and reflected beams. Intensity basedsensors measure the light lost from the optical fiber.

One type of optical sensor is the extrinsic Fabry-Perot interferometer(“EFPI”). An EFPI utilizes two reflective surfaces and the difference orshift between a reference beam and a reflected beam directed through anoptical fiber. This phase shift is used to determine or calculate thedesired physical or environmental characteristic.

Optical sensors can be used in manufacturing, aerospace applications,civil engineering applications and medical applications. In thepetroleum industry, for example, it is important from at least a safetyand environmental standpoint to obtain accurate pressure informationduring, for example, the drilling of an oil well, because the drill bitmay drill into a high pressure layer. Optical sensors are lowered intothe oil wells during drilling and completion of oil wells to communicatepressure information from various depths within the wells.

Co-locating dual optical sensors have been discussed in the patentliterature. For example, both U.S. Pat. Nos. 5,682,237 and 6,671,055 B1disclose interferometric spectrum from etalons of reflected lightportions from co-locating sensors. The disclosures of these referencesare incorporated herein by reference in their entireties. Suchapplication has not extended into the petroleum industry due to thesevere environment encountered downhole. For example, U.S. Pat. No.6,563,970 B1 discloses an optical sensor for use in an oil and gas wellthat requires a complex pressure transducer to apply downhole pressureto either elongate or compress a fiber having a Bragg grating thereon.

Additionally, known EFPI sensors used in petroleum drilling only measureone parameter, e.g., either temperature or pressure. However, thetemperature within an oil well increases with increasing depth, andoptical sensors are susceptible to temperature changes. Failure toaccount for these temperature changes can lead to inaccurate pressurereadings.

Therefore, the need exists for a suitable optical sensor that detectsboth pressure and temperature in wellbores to provide correction ofpressure measurements based upon the measured temperature.

SUMMARY OF THE INVENTION

The present invention is directed to an optical sensor adapted for usein the oil and gas wells that has at least two sensing regions. Eachsensing region preferably measures one environmental condition, e.g.,pressure, temperature, tilt angle of the well bore, position, vibration,acoustic waves, chemicals, chemical concentrations, current, electricfield and strain, among other properties. Preferably, the two or moresensing regions are located proximate to each other so that the measuredenvironmental conditions are at substantially the same depth. Eachsensing region may include an intrinsic type sensor or an extrinsic typesensor or both.

The present invention is directed to an optical sensor comprising atleast two sensing regions located proximate to each other. One of thesensing regions is a pressure sensing region and comprises a sealedcavity having a first and second reflecting surfaces. The distancebetween the first and second reflecting surfaces changes in response toa change in pressure, and a first reflected light and a second reflectedlight from these two reflecting surfaces form an interferometric signalrepresentative of a pressure at the location of the optical sensor.

A launch waveguide is operatively connected to the sealed cavity andprojects light into the sealed chamber. The launch waveguide can beconnected to the cavity or be spaced apart therefrom. The sealed cavityhas various configurations. It can be defined by a hollow tube, thelaunch waveguide and a distal member, where the tube is sealed to thelaunch waveguide and the distal member. The distal member can be areflective waveguide, an end cap or a disk. In other configurations, thesealed cavity can be defined by an end cup sealed to the launchwaveguide or by two half-cups sealed to the launch waveguide. The cavitycan be sealed by conductive heating, arc welding, laser welding, FRITglass, solder glass, molecular polishing, epoxy, adhesive or anodicattachment. The sealed cavity can comprise a gas or can be a partialvacuum. The partial vacuum can be provided by vacuum fixturing processor by gas diffusion process.

The other sensing region of the optical sensor can be a temperaturesensing region, which comprises a temperature sensitive material. In oneembodiment, the temperature sensing region comprises a third reflectingsurface. The second reflected light and a third reflected light from thethird reflecting surface form an interferometric signal representativeof a temperature at the location of the optical sensor. In anotherembodiment, the temperature sensing region further comprises a fourthreflecting surface and wherein a third reflected light and a fourthreflected light from the third and fourth reflecting surfaces form aninterferometric signal representative of a temperature at the locationof the optical sensor. The first and second reflecting surfaces can beconnected to the third and fourth reflecting surfaces by a reflectivewaveguide.

The temperature sensing region can be located within the sealed cavity,can be spaced apart from the sealed cavity, or can form a part of thewall of the cavity.

In one embodiment, the second and third reflecting surfaces define adiaphragm and in response to pressure the diaphragm changes the distancebetween the first and second reflecting surfaces. In another embodiment,the sealed cavity has a unitary construction and is defined by a tubefused to the launch waveguide and to a capillary tube. Preferably, thetube and the capillary tube are made from materials having similarcoefficient of thermal expansion, or from the same material tocompensate for the thermal expansion on the distance between the firstand second reflecting surfaces. A temperature sensing material can bedisposed inside the capillary tube. The capillary tube may comprise ahollow portion to minimize reflected light. Alternatively, the distalend of the capillary tube is modified to minimize reflected light.

In another embodiment, the launch waveguide is spaced apart from thesealed cavity and projects light into the sealed cavity. The distal endof the launch waveguide can be angled so that light propagating throughthe launch waveguide is directed into the cavity. The sensor can be madefrom wafers that are polished to a molecular level so that the wafersare bonded to each other. The wafers then can be diced or cut up intoindividual sensors and attached to launch waveguides.

Light from the launch waveguide can propagate through the temperaturesensing region before propagating through the pressure sensing region,and vice versa. One of the first and second reflecting surfaces can becoated with an optical coating. Alternatively, both of the reflectingsurfaces are coated with different optical coating.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings, which form a part of the specification andare to be read in conjunction therewith and in which like referencenumerals are used to indicate like parts in the various views:

FIG. 1 is a cross-sectional view of an optical sensor constructed inaccordance with an exemplary embodiment of the invention;

FIG. 2 is an enlarged view of the interface between the launch andreflective fibers of the optical sensor of FIG. 1;

FIG. 3 is an enlarged view of an end of the reflective fiber of theoptical sensor of FIG. 1;

FIGS. 4A-D illustrate the formation of an optical sensor in accordancewith another exemplary embodiment of the invention;

FIG. 5 is an enlarged view of the interface between the launch andreflective fibers of the optical sensor of FIG. 4D;

FIGS. 6A-B illustrate another optical sensor of the present invention;

FIG. 7 is a cross-sectional view of another optical sensor of thepresent invention showing dual cavities;

FIGS. 8A-D illustrate the formation of another dual cavity opticalsensor of the present invention;

FIG. 9 is a cross-sectional view of another optical sensor;

FIG. 10 is a cross-sectional view of another optical sensor;

FIG. 11 is a cross-sectional view of another optical sensor;

FIG. 12 is a cross-sectional view of another optical sensor;

FIG. 13 is a cross-sectional view of another optical sensor;

FIGS. 14A-14C are cross-sectional views and cut-away view of anotheroptical sensor;

FIG. 15 is a cross-sectional view of another optical sensor, wherein thelaunch fiber is mechanically decoupled from the sensing regions;

FIG. 16 is an exploded perspective view of the optical sensor of FIG.15;

FIG. 17 is a cross-sectional view taken along line 17-17 of FIG. 16.

FIG. 18A illustrates a partial wafer including the lids of FIG. 15; FIG.18B illustrates a partial wafer including the bodies of FIG. 15; FIG.18C illustrates a partial wafer including the upper retaining mechanismsof FIG. 15;

FIG. 19 illustrates a process for assembling the optical sensor of FIG.15;

FIG. 20 illustrates schematically a fiber optic system incorporating theoptical sensors of the present invention;

FIG. 21 is a graph indicating spectral data taken by a sensor of FIG. 1;

FIG. 22 is a graph of the spectral data of FIG. 10 converted by Fouriertransform;

FIG. 23 is a graph of the spacing of reflective surfaces versuspressure;

FIG. 24 is a graph of the pressure gap versus pressure at varioustemperatures;

FIG. 25 is a graph of pressure error versus pressure for severaltemperatures; and

FIG. 26 is a graph of temperature gap versus temperature for a pressureindependent temperature measurement.

DETAILED DESCRIPTION

Referring initially to FIG. 1, an embodiment of optical sensor 10 inaccordance with the present invention includes tube 12, which has firstend 14 and second end 16 and relatively thick wall 18 extending betweenthe two ends. Tube 10 defines cavity 20 therewithin. At least oneinput/output or launch waveguide or fiber 22 is inserted into cavity 20at first end 14 and reflective waveguide or fiber 26 is inserted intocavity 20 at second end 16. The term “waveguide” and “fiber” are usedinterchangeably herein and include, but are not limited to, any opticalfiber, optical waveguide, fiber core, fiber core plus cladding and anyoptical structure capable of transmitting light. First end 24 of launchfiber 22 is spaced apart from first end 28 of reflective fiber 26 byspatial gap 21 having a length “L”. Second end 30 of reflective fiber 26is attached to cap 48. Cap 48 contains a temperature sensitive materialtherewithin and has distal end 50. Although cavity 20 and gap 21illustrate an EFPI and cap 48 illustrates a particular temperaturesensor, these sensors are used for illustration purpose only and othertypes of sensors are usable with the present invention. Hence, thepresent invention is not limited to any particular type of opticalsensor.

Launch fiber 22 is capable of transmitting multiple wavelengths of lightalong its length in both directions. Suitable materials for launch fiber22 include a single mode fiber, a multimode fiber, a polarizationmaintaining fiber or a plastic fiber, among others. The length of launchfiber 22 is selected based upon the particular application and thedistance to the depth being measured, e.g., the distance down an oil orgas well. Fiber 22 can have any diameter suitable for the particularapplication. In one non-limiting example, the diameter can be from about60 μm to about 250 μm, and preferably it is about 125 μm.

Suitable materials for reflecting fiber 26 include a coreless fiber, asingle mode fiber, a multimode fiber, a polarization maintaining fiberand a plastic fiber. Preferably, the length of reflective fiber 26 isrelatively short, so that the temperature sensor or cap 48 attached tosecond end 30 of reflective fiber 26 is located proximate to thepressure sensor located in tube 12. Fiber 26 may have the same diameteras fiber 22 or different diameter.

First end 24 of launch fiber 22 and/or first end 28 of reflective fiber26 can be modified to simulate or provide additional optics or opticaleffects. For example, first ends 24 and 28 can be modified to form orfunction as one or more lenses, providing a wider range of useful gaps21. In addition, optical coatings 23 and 27 can be applied to launchfiber first end 24 and reflective fiber first end 28, respectively.Optical coatings 23 and 27 enhance the spectral characteristics so thatdemodulation of the gap information may be more accurately and moreeasily accomplished. Optical coatings can be used to increase thefinesse of cavity 21, i.e., changing the shape or curves of a particularreflected light portion to distinguish it from the other reflected lightportions, and to allow wavelength division multiplexing. Suitablematerials for the optical coatings include, but are not limited to,magnesium fluoride, metal oxides (such as silicon monoxide, zirconiumoxide, tantalum oxide, niobium oxide, silicon carbide, aluminum oxide,etc.), silicon, gold, aluminum, titanium, nickel, chromium andcombinations thereof. Optical coatings 23 and 27 can be made from thesame material, and preferably from different materials.

To control length “L” of gap 21, launch fiber 22 can be attached to tube12 at first end 14 by one or more first bonds 32. Similarly, reflectivefiber 26 can be attached to tube 12 at second end 16 by one or moresecond bonds 34. Suitable methods for forming the first and second bonds32 and 34 include conductive heating, arc welding, laser welding, orthrough FRIT glass or solder glass. Alternatively, the bonds can bemolecular, epoxy, adhesive or anodic attachment mechanisms. Launch fiber22 and reflective fiber 26 can extend into cavity 20 and at least aportion of launch fiber 22 and a portion of reflective fiber 26 aredisposed within cavity 20. Length “L” of gap 21 can be defined as thedistance between launch fiber 22 and reflective fiber 26 within cavity20 or as the distance between the two first ends 24 and 28.

Referring to FIG. 2, light from a light source located on the surfacenear the wellhead propagates through launch fiber 22, and exits firstend 24 and enters gap 21 of cavity 20. Light includes any wavelength inthe electromagnetic spectrum, including but not limited to broadband,lasers, visible light, non-visible light. Initial light portion 36 istransmitted through launch fiber 22. As initial light portion 36contacts the interface at first end 24 between launch fiber 22 and gap21, a portion, for example approximately four percent, of initial lightportion 36 is reflected back down launch fiber 22 as first reflectedlight portion 38. First reflected light 38 has the same properties asinitial light 36 and is essentially the reference light. The percentageof reflected light is a function of material properties and dimensions,and the actual reflected percentage changes accordingly. First remaininglight portion 39 propagates through gap 21. At the interface at firstend 28 between gap 21 and reflecting fiber 26, another portion, forexample approximately four percent, is reflected back as secondreflected light portion 40. Second remaining light portion 42 propagatesthrough reflective fiber 26.

Referring to FIG. 3, second remaining light portion 42 propagates downreflecting fiber 26 toward second end 30. At the interface at second end30 between reflective fiber 26 and temperature sensitive cap 48, anotherportion, for example approximately sixteen percent, is reflected backalong reflective fiber 26 as third reflected light portion 44. Thirdremaining light 45 travels through cap 48. At distal surface 50 of cap48, another portion, for example approximately sixteen percent of light,is reflected back as fourth reflected light portion 46. The temperaturesensitive material can also have a metallic layer (not shown) disposedadjacent cap 48.

The reflected light portions 38, 40, 44 and 46 produce aninterferometric signal, which can be processed to yield the measuredproperties, e.g., pressure and temperature, discussed in details below.An example of such interferometric signal is disclosed in U.S. Pat. No.6,671,055 B1. The '055 patent is incorporated herein by reference in itsentirety. Furthermore, as discussed above it is noted that percentage ofreflected light is determined by the ratio of the index of refraction ofthe temperature sensitive material to the index of refraction of thesurrounding medium. Hence the exemplary percentages of reflected lightportions provided above are for illustration purpose only.

As optical sensor 10 descends into a well, pressure “P” (shown inFIG. 1) is uniformly exerted along the entire exterior of tube 12. Aspressure “P” increases, the exterior is pushed inwardly, changing gap 21of cavity 20. In particular, the pressure increases (with increasingdepth from the surface) length “L” of gap 21 decreases. This change inlength “L” is used to calculate the pressure at any point within thewell. In one embodiment, length “L” of spatial gap 21 is pre-determinedto correspond to a pre-determined pressure. Specifically, the initiallength of gap 21 is chosen so that interferometric measurement of theoptical displacement between the launch fiber first end 24 and areflective surface corresponds to a known pressure, such as, forexample, standard pressure of 14.7 pounds per square inch (psi). Gap 21can be a partial-vacuum, and may contain an inert gas or air. Theresidual gas can be removed by vacuum fixturing, gas diffusion processor other known techniques. In the gas diffusion process, cavity 20 isfilled with helium (He) and as helium diffuses from the cavity a partialvacuum is formed within gap 21. In vacuum fixturing, cavity 20 is influid communication with a capillary tube, and the gas in cavity 20 canbe withdrawn through the tube and the tube is sealed or pinched tomaintain the partial vacuum in the cavity.

As was discussed previously, end cap 48 is formed of a material 52 thatexhibits a changing refractive index with changing temperature. Thus, asoptical sensor 10 descends from the surface, the refractive index of cap48 changes with the increasing temperature, thus altering the opticaldisplacement between second end 30 and distal cap surface 50 as shown inFIG. 3. The difference in the optical displacements at the earth'ssurface and at some depth below the surface is equated with atemperature at that depth. Knowing the temperature at a given depthallows for the correction of the pressure calculations to moreaccurately portray the pressure at that same depth and for thecorrection of thermal apparent error. Alternatively, the temperaturesensitive material can be viewed as a filter having a wavelength thatchanges with temperature.

Temperature sensitive material 52 in cap 48 can be constructed from anymaterial, or combination of materials, that exhibits a changing opticalpath resulting from changing index of refraction and/or coefficient ofthermal expansion with changing temperature. In other words, as theindex of refraction changes the speed of light through the medium alsochanges resulting in a phase change. This phase change causes a changein the interference of the reflected light at the temperature materialwith the reflected light at the pressure gap, which is the readableinterferometric result. As used herein, with respect to temperaturesensitive materials, the optical displacement of a material refers tothe effect of the index of refraction of that material on the speed oflight propagating through the material. Suitable temperature sensitivematerials include, but are not limited to, silicon, sapphire, siliconcarbide (SiC), tantalum oxide (Ta₂O₅) and others, such as metal oxides.Such temperature measurement is disclosed in, J. Sotomayor and G.Beheim, “Laser-Annealed Fabry-Perot Fiber-Optic Temperature Sensor”published in SPIE Vol. 2070-Fiber Optic and Laser Sensors XI (1993). Thedisclosure of this reference is incorporated herein in its entirety.

Hence, in the embodiment of FIGS. 1-3, one sensing region includes thepressure measurement resulting from first reflected light 38 and secondreflected light 40, i.e., gap 21, and the other sensing region includesthe temperature measurement resulting from third reflected light 44 andfourth reflected light 46, i.e., end cap 48.

In accordance with one aspect of the present invention, at least one oflaunch fiber 22, reflecting fiber 26, tube 12, cap 48 and othercomponents comprises a coating arranged to shield the fiber or tube frommoisture or other contaminant to improve stability and reliability.Suitable coatings include xylylene (available as Parylene®), carbon,titanium oxide and combinations thereof.

Sensor 10 can be manufactured by many techniques and have otherconfigurations. Another exemplary, non-limiting technique is illustratedin FIGS. 4A-4D and 5. Tube 12 with wall 18 and cavity 20 can beconstructed from any material that deforms when exposed to increasingpressure, preferably within the pressure range that sensor 10 operates.Suitable materials for tube 12 include metal, polymer, sapphire,alumina, and combinations thereof. Tube 12 can be extruded, drawn orpierced. Although cavity 20 can be arranged to have any shape desired,cavity 20 is generally cylindrical in shape, and tube 12 may containmore than one cavity 20. Cavity 20 should have an inner diameter thatcan accommodate both launch fiber 22 and reflective 26. Temperaturesensitive material 52 is inserted into cavity 20, as illustrated in FIG.4A. The temperature sensitive material is etched down to a remainingportion 52′, as illustrated in FIG. 4B. When temperature sensitivematerial 52 is silicon, potassium hydroxide (KOH) can be used as theetching medium.

Disk 54 is then attached to tube 12 and is flushed with remainingtemperature sensitive material 52′, as illustrated in FIG. 4C. Disk 54can be attached by any means, such as, laser welding or solder glass.Disk 54 can be made from a similar material as tube 12. Thereafter,launch fiber 22 is inserted into cavity 20 until first end 24 of launchfiber 22 is spaced apart at length “L” in spatial gap 21 from remainingtemperature sensitive material 52′, as illustrated in FIG. 4D. Launchfiber 22 can be attached to tube 22 by bond 32 or 34. Hence, theembodiment of sensor 10 shown in FIGS. 4A-4D differs from the embodimentshown in FIGS. 1 in that the temperature sensitive material is protectedinside tube 12 and that reflective fiber 26 is also omitted. Launchfiber 22 may include optical coating 23, and temperature sensitivematerial 52, 52′ may include an optical coating 27.

The optical path of the embodiment of FIGS. 4A-4D is shown in FIG. 5.Initial light portion 36 propagates along launch fiber 22 and ispartially reflected at first end 24 of fiber 22. First reflected light38 is reflected back in the opposite direction along launch fiber 22.First remaining light portion 39 propagates through spatial gap 21 andis partially reflected at first end 56 of temperature sensitive portion52′. Second reflected light 40 is reflected back through gap 21. Secondremaining light 42 propagates through temperature sensitive portion 52′and is partially reflected at second end 58 as third reflected lightportion 44. Again, the reflected light portions produce aninterferometric signal, which can be interpreted to yield the measuredproperties, e.g., pressure and temperature, discussed in details below.

Hence, in the embodiment of FIGS. 4A-4D and 5, the first sensing regionincludes the pressure measurement resulting from first reflected light38 and second reflected light 40 and the other sensing region includesthe temperature measurement resulting from second reflected light 40 andthird reflected light 44.

Another embodiment of sensor 10 is shown in FIGS. 6A-6B. Optical sensor10 includes cap 48 that is separate from and independent of tube 12. Cap48 has a cavity that contains temperature sensitive material 52.Temperature sensitive material 52 is lapped down flat so that leadingfirst end 56 is generally flat and aligned with cap 48's edge. Cap 48 isbonded to tube 12 so that temperature sensitive material 52 is exposedto tube cavity 20. Suitable methods for bonding cap 48 to tube 12 arethe same as those for attaching disk 54 to tube 12. In this embodiment,launch fiber 22 is inserted into the cavity 20 in a similar manner asthe embodiment of FIGS. 4A-4D to create gap 21 and is secured and bondedin that position by bond 32 or 34. The optical path of the embodiment ofFIGS. 6A-6B is substantially similar to that of the embodiment of FIGS.4A-4B.

Although illustrated above in FIG. 1 with a single set of gap 21, launchfiber 22, temperature sensitive material 52 and reflecting fiber 26,sensor 10 can include two or more sets of launch fibers, gaps,temperature sensitive materials and reflecting fibers. Referring to FIG.7, optical sensor 10 includes two launch fibers 22 fixedly securedwithin two spaced apart cavities 20 of tube 12. Alternatively, launchfibers 22 can be disposed within a single cavity 20. Two reflectingfibers 26 can be securely attached to tube 12 creating a pair of gaps21. Launch fibers 22, reflective fibers 26 and gaps 21 can be identicalto provide redundancy or can be different to provide for comparativemeasurements. For example, optical sensor 10 can be formed with twopressure gaps of different initial lengths and two temperature sensitivematerials of different optical lengths (or of different materials). Thelengths differ by a pre-determined ratio. By forming the optical sensor10 in this manner, additional information can be obtained from thesensor. Reflective caps 48 are provided at each second end 30 ofreflecting fibers 26 and can be constructed from the same temperaturesensitive material 52 or different temperature sensitive materials 52.

Another embodiment of sensor 10 utilizing two or more sets of sensingregions is illustrated in FIGS. 8A-D. This embodiment is similar to thesingle cavity embodiment of FIGS. 4A-4B, except that tube 20 has twocavities 20. Each cavity 20 of tube 12 is filled with temperaturesensitive material 52, and temperature sensitive material is etched downas was done with the single cavity embodiment. Disks 54 are bonded totube 12 at the end where the temperature sensitive materials 52′ arelocated (FIG. 8C). Then, launch fibers 22 are inserted into cavities 20and bonded into place. As was described above, temperature sensitivematerials 52 and lengths “L” of gaps 21 can be the same or different.

FIG. 9 illustrates another embodiment of sensor 10. In this embodiment,temperature sensitive material 52 is disposed in cavity 20 and at firstend 28 of reflecting fiber 26, and can be arranged as chip 60. Suitablematerials for chip 60 include silicon and the other temperaturesensitive materials discussed above. In addition in this embodiment,second end 30 of reflecting fiber 26 can be modified, such as bent,tapered, angled, crushed or polished, to reduce or to minimize anyadditional, unwanted reflections from the far end of reflecting fiber 26that may increase errors in the demodulation calculations. The opticalpath of this embodiment is similar to that of the embodiment of FIGS.4A-4D and 5, i.e., based on three reflected light portions.Alternatively, sensor 10 of this embodiment can be made from a metalsuch as titanium (Ti). More particularly, tube 12 and member 26 are madefrom a metal and are welded together at joint 34, and launch waveguide22 can be encased or protected by a metal sheath, which can be welded tometal tube 12 at joint 32. A metal construction can advantageouslyhigher pressure.

In another embodiment of optical sensor 10 illustrated in FIG. 10, cap48 is attached directly to launch fiber 22 and is constructed fromtemperature sensitive material 52, preferably silicon. Launch fiber 22can be attached to cap 48 by bond 32 or 34, or by using molecular,epoxy, or anodic attachment mechanisms. Launch fiber 22 can include core62 surrounded by cladding 64. Cap 48 is configured such that gap 21 isformed between first end 24 of launch fiber 22 and leading or first edge56 of temperature sensitive material 52. Length “L” of gap 21 is thesame as other embodiments. In addition, the thickness of cap 48 betweenfirst end 56 and second end 58 (which in this embodiment is the same asdistal cap surface 50) of temperature sensitive material 52 is selectedso that the end of cap 48 acts like a pressure sensitive diaphragmconfigured to flex due to the pressure acting upon distal cap surface 50for the pressure ranges in which optical sensor 10 is deployed. Flexingof this diaphragm causes a change in length “L” of gap 21.

In the embodiment of FIG. 10, initial light portion 36 is transmitteddown core 62, and first reflected light portion 38 is reflected backthrough core 62 at first end 24 of launch fiber 22. Similarly, secondreflected light portion 40 is reflected at first end 56 of temperaturesensitive material 52 back through core 62. Length “L” is known atstandard pressure, and external pressure applied to distal cap surface50 flexes the pressure sensitive diaphragm and changes length “L” of gap21, resulting in a change in the interference pattern between firstreflected beam 38 and second reflected beam 40. This change ininterference pattern is used to calculate the external pressure appliedto cap surface 50.

In addition, third reflected light portion 44 is reflected at second end58 of temperature sensitive material 52 (or distal cap surface 50) backthrough core 62. The amount of time that it takes for light to passthrough temperature sensitive material 52 changes with the refractiveindex of the material, which changes with temperature. Therefore, as thetemperature in which optical sensor 10 is located changes, theinterference pattern between third reflected light portion 44 and eitherfirst reflected light portion 38 or second reflected light portion 40changes. This change is used to calculate the ambient temperature.

The optical path of this embodiment is similar to that of the embodimentof FIGS. 4A-4B, except that a single sensing element, the pressuresensitive diaphragm at distal end 50 of cap 48, measures both thepressure and temperature.

In another embodiment illustrated in FIG. 11, optical sensor 10 isconstructed without using bond 32 or 34. Optical sensor 10 has a unitaryconstruction and comprises launch fiber 22, gap 21 having length “L”,and a length of temperature sensitive waveguide or fiber 66 disposedinside capillary tube 68. Launch fiber 22 has core 62 and cladding 64.Both cladding 64 of launch fiber 22 and capillary tube 68 are fused totube 12 to provide the unitary construction. Similar to the embodimentof FIGS. 1-3, tube 12 defines cavity 20 and both launch fiber 22 andcapillary tube 68 partially extend into cavity 20. Preferably, capillarytube 68 extends into cavity 20 along most of the length of cavity 20, asshown, and both tube 12 and capillary tube 68 are made from the samematerial. When both tube 12 and capillary tube 68 are made from the samematerial and have the same coefficient of thermal expansion, tube 12 andcapillary tube 68 thermally expand at substantially the same amount,thereby minimizes the effect caused by differential thermal expansion onthe changes of length “L” of gap 21. Hence, changes in length “L” wouldbe caused primarily by changes in pressure. Preferably, tube 12 andcapillary tube 68 are made from fused silica. Preferably, fiber 66 ismade from a fused silica based fiber which has sufficiently high dN/dT(change in index of refraction/change in temperature) for temperaturesensing.

Similar to the other embodiments of the present invention, initial light36 propagates along core 62 of launch fiber 22 and at first end 24,first reflected light portion 38 propagates back along core 62. Acrossgap 21, second reflected light portion 40 is reflected back at first endsurface 28 of waveguide 66. The transition from solid waveguide 66 tohollow portion 70 of capillary tube 68 provides reflective surface 30for third reflected light 44 to reflect back. Hollow portion 70 absorbsthe remaining light to minimize additional unwanted reflection and thedistal end of capillary tube 68 is bent, tapered, angled or otherwisemodified to absorb additional light. As discussed before, reflectedlight portions 38 and 40 produce interferometric signals to providepressure measurements, and reflected light portions 40 and 44 produceinterferometric signals to provide temperature measurements.

In the embodiment of FIG. 11, an intrinsic Fabry Perot interferometer orIFPI (temperature sensitive waveguide or fiber 66 disposed insidecapillary tube 68) is incorporated to an EFPI (gap 21) to form aco-located dual sensor. This embodiment allows the IFPI to besufficiently short for non-aliased interrogation, allows non-adhesiveattachment of the temperature sensor to the pressure sensor and retainsthe pressure insensitivity of the sensor. Depending on the laser systemused, the IFPI can be less than about 5 mm.

FIG. 12 illustrates another sensor 10, which is a variation of theembodiment of FIG. 11. In this embodiment, sensor 10 also comprises anIFPI temperature sensor incorporated to an EFPI pressure sensor. Tube 12is fusion bonded to cladding 64 of launch fiber 22 and to capillary tube68 at fusion joints 72. Similar to the embodiment of FIG. 11, thissensor has a unitary construction since tube 12 is fused to launch fiber22 and capillary tube 68, and instead of employing hollow section 70 toreduce further reflection after second reflective surface 30, in theembodiment of FIG. 12 capillary tube 68 cleaved, polished or coated witha metal, e.g., gold (Au) at end 74 after second reflective surface 30 tominimize additional reflection. Additionally, since hollow section 70 isnot used more temperature sensitive fiber 66 can be used. Sensor 10 ofthis embodiment can also be made from metal similar to sensor 10 of theembodiment of FIG. 9, discussed above.

Another embodiment of sensor 10 is illustrated in FIG. 13. In thisembodiment, the first sensing region comprises gap 21, which ispreferably made from a solid light transmitting material, and the secondsensing region comprises temperature sensitive material 52. Unlike theother embodiments gap 21 is solid and is not filled with gas or not apartial vacuum. Preferably, gap 21 is made from a borosilicate glass,which has a low coefficient of thermal expansion (CTE) to minimize theeffect of temperature the pressure measurement. Borosilicate glass canbe attached to launch fiber 22 by fusion bonding or fusion splicing.Borosilicate glass is resistant to chemical attack and the low CTEallows the pressure sensing region to be made thick. As such, thismaterial is suitable for deployment in an oil or gas well. Borosilicateglass is commercially available from Corning Glassware, Inc., as PyrexBrand 7740 Glass. Other glass having similar properties can also beused. The temperature sensing region can be made from any of thetemperature sensitive materials 52 discussed above, but preferably ismade from silicon. The temperature sensitive material 52 can be attachedto the pressure sensing region by any of the bonds 32 or 34 discussedabove, but preferably by anodic bonding. At least one of the launchfiber, pressure sensing region or temperature sensing region can becoated with one or more of the coatings discussed above.

Preferably, gap 21 can have the same diameter as launch fiber 21 orlarger. Length “L” can be adjusted to provide suitable changes in lengthdue to pressure for a particular application. Light propagating downcore 62 would provide reflected light portions 38, 40 and 44 at surfaces24, 28 and 30, respectively.

Another embodiment of sensor 10 is illustrated in FIG. 14A-14C. Thisembodiment is similar to the embodiment of FIG. 10 with a pressuresensitive diaphragm. In this embodiment, sensor 10 comprises twohalf-cups 76 and 78 made from temperature sensitive material 52 andpreferably silicon. First half-cup 76 defines a hole sized anddimensioned to receive launch fiber 22. First half-cup 76 also has aninternal cavity adapted to receive washer 80. Washer 80 preferably ismade from a doped glass (silica) and also has a hole to receive launchfiber 22. Washer 80 assists in the bonding of launch fiber 22 to firsthalf cup 76.

To assemble the sensor, launch fiber 22 is inserted through firsthalf-cup 76 and washer 80, and the assembly is heated in an inert gasatmosphere to the softening point of washer 80. The assembly is thencooled below this softening point and an electrical charge is applied toanodically bond washer 80 to half-cup 76 and to launch fiber 22. Secondhalf-cup 78 can be bonded to first half cup 76 by bond 32, 34.Alternatively, as shown in FIG. 14C washer 80 can have the same diameteras half cups 76 and 78, so that the two half-cups can be anodicallybonded to each other. Launch fiber 22 may terminate flushed with washer80 or can protrude beyond washer (as shown) or may terminate withinwasher 80.

In this embodiment, the pressure sensing region comprises gap 21 havinglength “L” and the temperature sensing region comprises temperaturesensitive material 52 of second half-cup 78, similar to the otherembodiments. Distal end 50 of second half-cup 78 acts as a diaphragm andthe diaphragm responses to pressure applied on distal end 50. Appliedpressure reduces length “L”, which can be processed to measure thepressure, and the change of index of refraction in second half-cup 78can be process to measure temperature, as discussed above.

Referring to FIGS. 15-17, another optical sensor 10 of the presentinvention is shown. In this embodiment, sensor 10 comprises bothpressure and temperature sensing regions. However, in this embodiment,the temperature sensing region is upstream of the pressure sensingregion and both regions are spaced apart from launch fiber 22. Sensor 10includes a lid 82, a body 84, and an upper retaining mechanism 86 and alower retaining mechanism 88. Upper and lower retaining mechanisms 86and 88 retain launch fiber 22. In this embodiment, launch fiber 22 ismechanically decoupled from the sensing regions.

Lid 82 is suitably configured and formed of a material which resistsbending due to pressure being acted upon it. In one exemplaryembodiment, lid 82 is formed of silicon and is thick enough to inhibitany significant flexing. The body 84 is attached to an underside surface83 of the lid 82 through a suitable attaching mechanism, such as, forexample, an adhesive.

Aperture 20 is formed through the body 84. On the underside surface 83of the lid 82 at a position contiguous with aperture 20, a firstreflective layer 92 is provided. First reflective layer 92 is formed ofa material which reflects substantially all light incident upon itssurface, such as gold (Au). As with the lid 82, body 84 is configuredand formed of a material which resists bending due to pressure beingacted upon it. In one exemplary embodiment, the body 84 is formed ofsilicon and is thick enough to inhibit any significant flexing of thebody 84.

Upper fiber retainer 86 includes a diaphragm 94 extending from an upperretaining base 96. As illustrated in FIG. 17, upper retaining base 96includes a V-groove suitably configured to retain launch fiber 22. Itshould be appreciated that upper retaining base 96 may take anyconfiguration capable of retaining launch fiber 22.

Diaphragm 94 is dimensioned and sized in area, shape and thickness toexhibit the necessary transfer function for pressure and temperature. Inparticular, diaphragm 94 is configured to be flexible in the presence ofpressure being acted upon it. Diaphragm 94 is formed of temperaturesensitive material 52, as described above. In an exemplary embodiment,upper fiber retainer 86, including the diaphragm 94, is formed ofsilicon.

Fiber 22 rests in and is further retained in lower retaining mechanism88. Lower retaining mechanism 88 includes another V-groove, asillustrated in FIG. 16, which matches the V-groove of upper retainingmechanism 86. It should be appreciated, however, that any suitableconfiguration may be used to retain launch fiber 22 in the lowerretaining mechanism 88.

Launch fiber 22 extends from a light source (not shown) to angled fiberend 98. Angled fiber end 98 is polished at an approximately 45° anglefrom the longitudinal axis of the fiber 22. Second reflective layer 93is coated on polished angled fiber end 98. Second reflective layer 93 isformed of a material which is capable of reflecting substantially alllight incident upon its surface, such as gold.

Next will be described the functioning of optical sensor 10. Initiallight 36 from the light source propagates down launch fiber 22. Initiallight 36 reaches second reflective layer 93 at angled fiber end 98 andis reflected approximately 90° to continue its transmission at an angleapproximately perpendicular to the longitudinal axis of launch fiber 22.

The V-grooves are formed so that the distance D between the outersurface of the fiber 22 and diaphragm 94 is sufficiently small so thatsubstantially no reflection of initial light transmission 36 occurs atthe outer surface of the fiber 40. Instead, first reflected light 38occurs at a lower surface 100 of diaphragm 94, and first reflected light38 is reflected off of second reflective layer 93 and back up launchfiber 22 to the surface. Second reflected light portion 40 occurs atupper surface 102 of the diaphragm 94, and this reflected light also isreflected off of second reflective layer 93 and back up launch fiber 22.Finally, third reflection 44 occurs at the first reflective layer 92 onthe underside surface of the lid 82, and that reflected light is alsoreflected off of second reflective layer 93 and back up launch fiber 22.Since first reflective layer 92 is formed of a material which reflectssubstantially all light becoming incident upon its surface, thirdreflection 44 contains substantially all the remaining light from theoriginal light transmission 36 less the light already reflected in thefirst and second reflections 38, 40.

An alternative embodiment of FIGS. 15-17 will now be described. Insteadof first reflective layer 92 on underside surface 83 of the lid 82, ananti-reflective coating may be positioned on an upper surface of the lid12. In such an embodiment, fourth reflection 46 would not reflect all ofthe remaining light, but would instead reflect about the same percentageas the other reflections 38, 40, 44. An antireflective coating on theupper surface of the lid 12 inhibits an additional reflection that mayinterfere with the accurate demodulation of the desired interferometricsignals.

As optical sensor 10 descends into a well, pressure causes the diaphragm24 to flex, creating a change in distance “L” between the upper surfaceof diaphragm 94 and first reflective layer 92 on the underside surface83 of the lid 82. As the pressure increases, the distance the light musttravel between the second and third reflections 40, 44 is altered. Thechange in this distance can be used to calculate the pressure at anypoint below the surface.

As noted above, diaphragm 94 is formed of a material that exhibits achange in refractive index with changing temperature. The timedifferential between the return of the first and second reflections 38,40 corresponds to a known temperature, such as, for example, standardtemperature of 70° F. at the earth's surface. As sensor 10 descends fromthe surface, the refractive index of diaphragm 94 will change with theincreasing temperature, thus altering the time differential between thefirst and second reflections 38, 40. The difference in the timedifferentials of the first and second reflections between the surfaceand at some depth below the surface can be equated with a temperature atthat depth. Knowing the temperature at that depth will allow for thealteration of the pressure calculations to more accurately portray thepressure at that same depth.

With reference to FIGS. 18A-C and 19, a method of assembling sensor 10is illustrated. Major portions of sensor 10 may be formed entirely outof silicon in a standard wafer fabrication assembly and assembled withlaunch fiber 22 in a standard connector fashion, thus enabling massproduction in a repeatable way with a high yield. As shown, a wafer 104is formed with a plurality of lids 82 patterned thereupon (FIG. 18A).Another wafer 106 is formed with a plurality of bodies 84, eachincluding an aperture 90, patterned thereupon (FIG. 18B). Another wafer108 also is formed with a plurality of upper fiber retainers 86patterned thereupon (FIG. 18C). The wafers 104, 106 and 108 are formedof a suitably crystalline material, such as, for example, silicon. It ispreferred that each of the wafers 104, 106 and 108 is formed of the samecrystalline material as the other wafers. It should be appreciated thatthe wafers 104, 106 and 108 and the lids 82, bodies 84, and upper fiberretainers 86 thereupon are only partially shown for ease ofillustration.

Referring to FIG. 19, at step 110, each of the wafers 104, 106 and 108are polished down to the molecular level. A lapping/polishing machine,such as a chemical mechanical polisher, may be utilized to polish thewafers 104, 106 and 108. By polishing each wafer down to the molecularlevel, the wafers are rendered smooth at the molecular level.

At Step 112, the wafers 104, 106 and 108 are all aligned and fusionbonded together. To ensure proper measurements and minimal degradationof the measurement quality of the sensors 10 formed through thisprocess, the alignment and fusion of the wafers 104, 106 and 108preferably should be accomplished in a vacuum. This will create a vacuumin apertures 90 in the body 84. Because each of the wafers 104, 106 and108 is smooth down to the molecular level, contact between them causesthe wafers to fuse together. For the wafers formed of silicon, thefusion bonding is a silicon fusion bonding.

At Step 114, the wafers 104, 106 and 108 are diced into individual dies,each including a lid 82, a body 84, and an upper fiber retainer 86. AtStep 116, lower retaining mechanism 88 is attached to upper retainingmechanism 86 for each of the now diced dies. A suitable attachmentmechanism is solder glass. The attachment of upper retaining mechanism86 to lower retaining mechanism 88 is removed a suitable distance fromthe diaphragm 94, thereby mechanically decoupling the mounting of launchfiber 22 from the sensing components of sensor 10.

At Step 118, launch fiber 22, with its angled end 98 already polishedand coated with second reflective layer 93, is positioned within theV-grooves of the retaining mechanisms 86, 88 and mounted therein.

In this way, launch fiber 22 is attached to sensor 10 in such a way thatit is mechanically decoupled from the measurement function of thesensor. Further, through the mass production of major components ofsensors 10, the cost of such sensors may be decreased, making the use ofsuch sensors 10 more economically feasible in lower producing wells. Itshould be appreciated that the lid 82, body 84 and upper fiber retainer86 can be lengthened to provide additional stress isolation between themounting and the sensing components of sensor 10.

With reference to FIG. 20, a fiber optic sensor system 120 is described.The fiber optic sensing system 120 includes a plurality of opticalsensors 10 mounted to launch fiber 22. A tap 122 can be included witheach sensor 10 to redirect any unreflected light to the next sensor 10along launch fiber 22. In this way, it is possible to string a pluralityof sensors 10 along launch fiber 22 to make temperature and pressuremeasurements at various locations along the well bore.

An exemplary method of operating sensor 10 of the present invention isdescribed below. Using co-located pressure and temperature sensor 10,pressure at a particular depth below the surface can be calculatedthrough the measurement of the optical displacements resulting from achange in the physical distance between the first pair of reflectionpoints when the index of refraction remains the same. Further, thispressure calculation can be modified to take into account a change intemperature experienced at that particular depth below the surface. Themodification is accomplished by measuring the optical displacementsresulting when the physical distance between the second pair ofreflection points remains largely unchanged due to the pressure, but theindex of refraction is altered.

Optical sensor 10 provides sets of reflective surfaces, the optical pathbetween which change with the application of pressure and temperature.Light reflected from sensor 10 interferes, and optically generatesinterferometric patterns/signals. An example of the interferometricspectrum is shown in FIG. 21. This interferometric spectrum isdemolulated mathematically through known signal transformationtechniques such as Fourier transform techniques or other mathematicalprocesses. Alternately, the interferometric spectrum may be demodulatedoptically using known optical path-length matching techniques.

The demodulated spectrum is shown in FIG. 22. The tip of each peak isthe approximate measured optical path length of each sensor signal. Thepeaks indicate the spacing locations of the reflective surfaces ofoptical sensor 10. As shown in FIG. 22, the locations of the reflectivesurfaces are at about 18, 53 and 71 on the horizontal axis.

The measured spacings are then converted to pressure and temperaturemeasurements using a calibration of optical sensor 10 over pressure andtemperature. A calibration of the sensor over pressure and temperatureis conducted and subsequently the locations of the reflective surfacescan be converted to pressure and temperature. A plot of detectedpressure versus spacing based on these peaks is illustrated in FIG. 23.Since the pressure gap measurement is dependent on temperature, thistemperature dependence is preferably determined and accounted for in thepressure calculations as discussed below.

Referring to FIG. 24, measured pressure gap 66 is plotted versuspressure for three different temperatures, e.g., 0° C., 75° C., 150° C.Any temperatures and any number of temperature curves can be used. Asshown, the three plots for the three temperatures do not overlap butdiverge, particularly at higher pressures. This represents a family ofpressure curves as functions of pressure gap and temperature. The errorin gap length is illustrated in FIG. 25. Gap error 68 resulting from thechange in temperature is calculated from a best fit straight line of thedata and plotted against pressure 62. A sensitivity of about 0.5 nm/psiyields an error of plus or minus 200 psi. Therefore, a plurality oftemperature dependent pressure calibration curves are needed to correctfor these gap errors, such as those shown in FIG. 24. Once thetemperature at the location of the pressure measurement is determined,then the appropriate pressure calibration curve is selected. Theselected pressure calibration curve is then used to determine thepressure associated with the measured pressure spacing. Alternatively,if the measured temperature does not match one of the curves, then twoadjacent curves that bracket are chosen, and the pressure reading isobtained by interpolation between these curves.

Preferably, a pressure independent temperature measurement from opticalsensor 10 is used. This temperature measurement can be carried out atthe ground surfaces and at known temperature, e.g., by measuring thechanges in optical length between surfaces 30 and 50 as shown in FIG. 3.FIG. 26 illustrates a suitable plot of measured temperature gap 70versus temperature 72 for a pressure independent temperaturemeasurement. In one non-limiting example, sensor 10 has a temperaturerange of 0-150° C., and a pressure range of 0-10,000 psi.

While the foregoing has described in detail exemplary embodiments of theinvention, it should be readily understood that the invention is notlimited to the disclosed embodiments. Rather the invention can bemodified to incorporate any number of variations, alterations,substitutions or equivalent arrangements not heretofore described, butwhich are commensurate with the spirit and scope of the invention.Accordingly, the invention is not to be seen as limited by the foregoingdescription, but is only limited by the scope of the appended claims.

1. An optical sensor comprising at least two sensing regions locatedproximate to each other wherein one of the sensing regions is a pressuresensing region and comprises a cavity having a first and a secondreflecting surface, wherein the distance between the first and secondreflecting surfaces changes in response to a change in pressure, andwherein a first reflected light and a second reflected light from saidreflecting surfaces form an interferometric signal representative of apressure at the location of the optical sensor, and wherein thereflected lights have substantially the same wavelengths as the originalincident light, and wherein the other sensing region is a temperaturesensing region substantially insensitive to pressure. 2-54. (canceled)55. The optical sensor of claim 1, wherein a launch waveguide isoperatively connected to the cavity and projects light into the chamber.56. The optical sensor of claim 55, wherein the cavity is defined by thelaunch waveguide and one of the following: a) a hollow tube and a distalmember, wherein the tube is connected to the launch waveguide and thedistal member, b) an end cap, or c) two half-cups.
 57. The opticalsensor of claim 56, wherein the distal member is a reflective waveguide,a disk or an end cap.
 58. The optical sensor of claim 1, wherein atleast one of the two reflecting surfaces is coated with an opticalcoating.
 59. The optical sensor of claim 1, wherein at least one of thetwo reflecting surfaces is modified.
 60. The optical sensor of claim 59,wherein at least one of the two reflecting surfaces forms a lens. 61.The optical sensor of claim 1, wherein said cavity comprises a partialvacuum.
 62. The optical sensor of claim 1, wherein said cavity comprisesborosilicate glass.
 63. The optical sensor of claim 1, wherein thetemperature sensing region comprises a third reflecting surface.
 64. Theoptical sensor of claim 63, wherein the second reflected light and athird reflected light from the third reflecting surface form aninterferometric signal representative of a temperature at the locationof the optical sensor.
 65. The optical sensor of claim 63, wherein thetemperature sensing region further comprises a fourth reflecting surfaceand wherein a third reflected light and a fourth reflected light fromthe third and fourth reflecting surfaces form an interferometric signalrepresentative of a temperature at the location of the optical sensor.66. The optical sensor of claim 65, wherein the first and secondreflecting surfaces are connected to the third and fourth reflectingsurfaces by an optical member.
 67. The optical sensor of claim 1,wherein the temperature sensing region is located within the cavity, orthe temperature sensing region is spaced apart from the cavity.
 68. Theoptical sensor of claim 1, wherein the temperature sensitive regionforms a part of the cavity wall.
 69. The optical sensor of claim 64,wherein the second and third reflecting surfaces define a diaphragm andwherein in response to pressure the diaphragm changes the distancebetween the first and second reflecting surfaces.
 70. The optical sensorof claim 55, wherein the cavity has a unitary construction and isdefined by a tube fused to the launch waveguide and to a capillary tube.71. The optical sensor of claim 70, wherein the tube and the capillarytube are made from materials having similar coefficient of thermalexpansion.
 72. The optical sensor of claim 71, wherein the length thatthe capillary tube extends inside the cavity is substantially close tothe length of the cavity to compensate for the thermal expansion on thedistance between the first and second reflecting surface.
 73. Theoptical sensor of claim 71, wherein the tube and capillary tube are madefrom fused silica.
 74. The optical sensor of claim 73, wherein thetemperature sensing region is disposed inside the capillary tube. 75.The optical sensor of claim 70, wherein the capillary tube furthercomprises a hollow portion to minimize reflected light.
 76. The opticalsensor of claim 70, wherein the distal end of the capillary tube ismodified to minimize reflected light.
 77. The optical sensor of claim55, wherein the launch waveguide is located spaced apart from the cavityand projects light into the cavity.
 78. The optical sensor of claim 77,wherein the distal end of the launch waveguide is angled so that lightpropagating through the launch waveguide is directed into the cavity.79. The optical sensor of claim 77, wherein light from the launchwaveguide propagates through the temperature sensing region beforepropagating through the cavity.
 80. The optical sensor of claim 1,wherein the sensor measures the pressure and temperature at apredetermined downhole location in an oil or gas well.
 81. The opticalsensor of claim 1, wherein the cavity is sealed.